1. Field of the Invention
The invention relates to a cycle, such as a bicycle, and, more particularly, to a device for adjusting the trail of the front wheel assembly of such cycle, as well as a wheel equipped with such device, and a method of using such device.
2. Description of Background and Other Information
With respect to bicycles in particular, some riders need to be able to adjust certain geometric parameters of the cycle, which affect the position of the bicycle and/or the behavior of the bicycle under various conditions. Although certain parameters, such as the height of the saddle, the height of the handlebar, etc., usually are easily adjustable, adjusting other parameters is generally impossible, complicated, or difficult without special tools.
In particular, the relative head position with respect to the front wheel considerably affects the dynamic behavior of the bicycle. Certain important parameters affecting this position include the rake angle and the trail.
FIG. 1 shows a front wheel, with radius R, mounted on a fork and supported on the ground P. The rake angle corresponds to the angle A representing the angle between the steering axis D and the ground plane P. The trail h corresponds to the distance measured on a horizontal ground plane P, between the steering axis D and the wheel contact point B on the ground plane P. The offset C, sometimes referred to as fork rake, with regard to bicycles, corresponds to the distance between the hub axis O and the steering axis D. All of these parameters are interdependent and affect the dynamic behavior of the bicycle. FIG. 1 also shows, at least in part, the head tube, the top tube, and the down tube of the bicycle frame. If the top tube is horizontal and parallel to the ground plane P, the angle A can also be regarded as the head angle.
FIG. 2 is a graph that shows the trail h varying as a function of the rake angle A for various values of offset C, namely, 46, 50, and 54 mm, respectively. The relationship between the rake angle A and the trail h is expressed as follows:h=(R·cos(A)−C)/sin(A)
The graph shows that a small change in rake angle produces a relatively substantial change in the length of the trail. For example, a 1 degree rake angle variation produces a change in trail on the order of 6 mm on the ground.
With respect to bicycle behavior, each of the rake angle and the trail significantly affects the stability of the bicycle. In particular, a small trail can translate, for example, into a tendency for the bicycle to wander somewhat when the rider is out of the seat, such as during climbing or sprinting. Physically, this can be explained by a decrease in the moment about the steering axis generated by the lateral force at the bicycle ground contact point. A small trail produces a sensation for the rider of the bicycle being lighter and more maneuverable, but also more sensitive, which can generate sudden and involuntary changes in direction or heading. Therefore, it requires the rider to be more vigilant, more careful, while riding.
Furthermore, under certain aerodynamic conditions, an increase in trail can be advantageous In order to reduce the lateral moment and, therefore, to reduce the bicycle wander. Conversely, if the trail is small, the bicycle tends to be subject to the strong forces of a lateral moment caused by a lateral wind, and its stability is thereby affected.
Finally, controlling the rake angle can be difficult when the bicycle is being manufactured due to manufacturing tolerances. However, as shown in the graph of FIG. 2, a small rake angle variation substantially affects the trail and, therefore, the dynamic behavior of the bicycle. Thus, it is important to be able to adjust the trail in order to compensate for the deviations that are due to manufacturing tolerances.
Therefore, there is a need to be able to easily and efficiently adjust these parameters that are related to the relative positions of the steering head and the wheel on the ground, for example, either as a function of the riding conditions, or in order to compensate for manufacturing tolerances.
Certain prior art documents have proposed solutions for adjustment in the field of motorcycles, which are quite complicated to implement. For example, the patent document FR 2 880 609 and family member US 2008/0018076 relate to an improvement to an adjustable rake device for a motorcycle, which uses an eccentric principle to adjust the rake angle in the area of the head tube. This solution has the drawback of requiring intervention in the area of the head, which is quite difficult to carry out and requires special tools.
The patent document DE 102 29 740 relates to the construction of a motorcycle front wheel assembly, in which the braking system and the wheel axle are adjustable using two eccentric means. This system is complex and requires angular control of the adjustment between the brakes and the wheel, which is not easy to achieve.
Other systems for adjusting a wheel axle with eccentric means are available, such as an axle sold under the trademark “e-Axle®” by the Rekluse Motor Sports Company, for example. As with the aforementioned device, precise adjustment of such a system is complicated.
The patent document WO 2006/056869 and family member US 2007/0262556 relate to a method and a device for a front wheel of a vehicle, such as a motorcycle, which includes an adjustment of the position of the wheel axle with respect to the fork support by means of a fitting positioned in an opening of the fork and including a seat arranged in a predetermined position with respect to the fork opening, in order to receive one of the ends of a rotational pin of the wheel axle, so that the seat of the fitting assumes a predetermined relative position, which is selectively adjustable with respect to the fork so as to adjust the position of the rotational pin with respect to the fork. However, such an adjustment system is complicated to implement for a bicycle. Another drawback is created by a fitting that is inserted between the fork opening and the axle rotational pin, which itself is positioned in the opening. The pin therefore exerts forces on the fitting in the area of its seat, which can cause wear and tear, as well as clearances in the area of the fork axle.